DESCRIPTION: The overall goal of this application is to evaluate the involvement of T cells in periodontal bone resorption. The applicants have demonstrated that antigen-specific-Thl T cell activation is necessary for bone resorption in the rat gingival challenge/ adoptive transfer periodontal disease model. There is a requirement of LPS for B7 expression by macrophage/dendritic cells(Mac) to activate the T cells. Osteoprotegerin-ligand(OPG-L) has been shown to be intimately associated with osteoclast differentiation. B7 co-stimulation and MHC dependent activation appear to induce maximal OPG-L expression by Thl cells. The plan is to use the disease model in congenitally athymic rats to facilitate recognition of transferred cell populations. In the first Specific Aim the involvement of OPG-L expressing T cells in periodontal bone resorption will be tested using a fusion protein(OPG-Fc) which blocks OPG-L mediated osteoclast differentiation. OPG-L expression in types of gingival and in naive T cells will be evaluated. B7 co-stimulatory expression after LPS/antigen stimulation on Mac in vivo and its role in OPG-L expression on T cells will be evaluated. The direct effects of OPG-L expressing gingival T cells on osteoclast differentiation will be determined. In the second Aim CD40-CD40L interaction that regulates antigen and B7 specific enhancement of OPG-L expression by T cells and subsequent bone resorption will be studied. This hypothesis will be tested by blocking CD40-CD40L engagement with anti-CD40L antibody. The presence of CD40L on gingival T cells and its relationship to B7 on Mac will be investigated by immunohistochemistry and immunofluorescence. Co-culture of primed (LPS/Omp) gingival Mac with T cells that leads to CD40L and OPG-L expression will be evaluated in vitro by blocking B7 or CD40L. The third Aim will determine some of the requirements for T cell entry into inflamed tissues and in the subsequent polarization of Th1 or Th2 cells in lesions. The hypothesis is that RANTES and other chemokines that bind to CCR5(associated with Th1 T cells) are responsible for polarization of antigen-primed Thl cells in inflammatory lesions where Thl cell OPG-L results in periodontal bone resorption. This will be investigated in vitro with antibody to chemokines involved in transendothelial migration of T cells and in vivo. The role of CCR5 blockade for Th1 polarization in periodontal lesions and on expression of OPG-L on polarized T cells migrating to gingivae will be explored. The goal is to provide insight into aspects of T cell involvement in periodontal bone resorption and to utilize steps in the pathways as targets for agents which may alleviate resorption.